1. Field of the Invention
The present invention relates to a digital signal processing method, a data recording and reproducing apparatus, and a data recording medium, and more particularly to a digital signal processing method, a data recording and reproducing apparatus, and a data recording medium that are suitable for signal processing on a high-density recording medium.
2. Description of the Related Art
Recently, data recording media have become denser. For example, as compared with a CD (Compact Disk), a DVD (Digital Versatile Disk) has a shorter minimum mark length and a higher track density with the track pitch of 0.74 μm that is shorter than half of that of a CD. The user recording capacity of a single-sided, single-layer DVD is 4.7 GB.
As a replacement of a disk in the current generation in which a red laser beam is used, manufacturers are now studying a next-generation super high-density optical disk that uses a violet laser beam (GaN). The user recording capacity of the next-generation optical disk is said to exceed 20 GB. Naturally, it will have a shorter minimum mark length and a shorter track pitch, each about half of that of the DVD. On such a high-density disk, a defect developed during disk manufacturing or dust or a scratch during use, if any, would be twice as large as that on the DVD in view of the relative data length.
For example, on a DVD, product coding (product coding is a coding of an error correction such as a product error correction coding) is performed for a set of 192×172 DVD data bytes to generate 10 columns of PI parity data for the rows and 16 rows of PO parity data for the columns, as shown in (A) in FIG. 1. As a result, a 208×182 bytes of ECC (Error Correction Code) block is built. Also, as shown in (B) in FIG. 1, one row of PO parity data is inserted every 12 rows to interleave data with PO parity data.
As shown schematically in FIG. 2, the first row to the 208th row of the first ECC block EB1 are written sequentially on a DVD, followed sequentially by the first row to the 208th row of the second ECC block EB2, and so on.
In this method, up to 16 rows may be erasure-corrected with PO parity data. This means that a disk error caused by a continuous disk defect of up to 6 mm in length may be corrected. A continuous error like this is called generally as a burst error. When the linear density is doubled in this format, the maximum length of a correctable defect will be reduced to 3 mm. On the other hand, five symbols (bytes) may be usually corrected with PI parity data and, if there is no random error, the maximum length of a correctable burst error on a DVD is about 10 μm. Therefore, when the linear density is doubled, the maximum length of a defect correctable with PI parity data will be reduced to 5 μm.
Therefore, if there is a random error, the length of a burst error correctable with PI and PO parity data becomes much shorter in the conventional digital signal processing method and on the data recording medium described above. It should be noted that DVD PO rows are interleaved with data rows, not to distribute burst errors, but to keep the parity data ratio constant and therefore there is no effect of increasing the correction length.
To solve this problem, the number of parity data units may be increased to make the correction length longer. However, this method is disadvantageous to high-density recording because parity data redundancy in the ECC block increases.